This invention relates to a fuel supply control method for electronically controlling the quantity of fuel being supplied to an internal combustion engine, and more particularly to a fuel supply control method of this kind, which is adapted to supply fuel to the engine in an amount appropriate to the magnitude of acceleration of the engine as desired by the driver, thereby improving the driveability of the engine at acceleration.
A fuel supply control system adapted for use with an internal combustion engine, particularly a gasoline engine has been proposed e.g. by Japanese Patent Provisional Publication (Kokai) No. 57-137633, which is adapted to determine the valve opening period of a fuel injection device for control of the fuel injection quantity, i.e. the air/fuel ratio of an air/fuel mixture being supplied to the engine, by first determining a basic value of the valve opening period as a function of engine rpm and intake pipe absolute pressure and then adding to and/or multiplying same by constants and/or coefficients being functions of engine rpm, intake pipe absolute pressure, engine cooling water temperature, throttle valve opening, exhaust gas ingredient concentration (oxygen concentration), etc., by electronic computing means.
According to this proposed fuel supply control system, the calculations of the valve opening period, i.e. fuel injection quantity and the operation of the fuel injection device are executed in synchronism with a top-dead-center (TDC) signal which is generated synchronously with rotation of the engine. When the magnitude of acceleration required for the engine to perform exceeds a predetermined value, such as at sudden acceleration, in addition to accelerating fuel quantity increase according to the above control synchronous with the TDC signal, another accelerating fuel quantity increase is applied at the same time, which is executed in synchronism with a control signal having a certain constant pulse repetition period and being independent of the TDC signal (asynchronous accelerating fuel quantity increase control), so as to make up for a shortage in the increasing fuel amount obtained by the TDC signal-synchronized control at acceleration of the engine, thereby enhancing the output characteristic of the engine.
According to this asynchronous accelerating fuel quantity increase control, the engine is determined to be in an accelerating condition wherein the same control is to be carried out, if the rate of change of the throttle valve opening, which is detected upon generation of each pulse of the above control signal with a constant pulse repetition period (hereinafter called "asynchronous control signal"), exceeds a predetermined value while the valve opening is increasing. Thus, only when the rate of change of the throttle valve opening is larger than the above predetermined value, the asynchronous accelerating fuel quantity increase control is effected. However, in suddenly snapping the engine or in stepping on the accelerator pedal to open the throttle valve to its maximum opening, the valve opening of the throttle valve can still assume a large value in the vicinity of the maximum opening position even when the rate of change of the throttle valve opening which has once been increased by the stepping-on of the accelerator pedal is afterwards decreased below the above predetermined value. On such an occasion, if the asynchronous accelerating fuel increase control is interrupted simultaneously when the rate of change of the throttle valve opening is decreased below the above predetermined value, a required increase in the engine output as desired by the driver cannot be achieved, thereby deteriorating the driveability of the engine.